Famciclovir is the prodrug form of penciclovir. Penciclovir is very similar to acyclovir in terms of mechanism of action and spectrum. Although it is much less potent than acyclovir, penciclovir accumulates to much higher concentrations inside the cell. Penciclovir has been studied in cats receiving famciclovir at 62.5 mg for 3 days; it appeared to be well tolerated.
Last full review/revision November 2015 by Dawn Merton Boothe, DVM, PhD